Loud-speaker motor



Jan. 13, 1931. w. AULL. J'R., ET AL 1,788,557

' ILOUD SPEAKER MOTOR Filed Sept. 4, 1928 2 Sheets-Sheet 1 INVENTORSJan. 13, 1931. w. uLL. JR. ET AL 1,788,557

LOUD SPEAKER MOTOR Filed,Sept. 4. 1928' 2 Sheets-Sheet 2 Patented Jan.13,

UNITED STATE-SPA T WILSON AULL, JR, or ASTOR-IA, AND HARRY-w. nouox, orMoimr vnnuou,

nEwYonK I I Application filed. September .'l.his invention relatestoielectromagnetic reproducers, and particularly applicable to loudspeakers such are used in radio broadcast reception, although itsapplication is not necessarily limited thereto. I

One object of this invention is to provide an electrical soundreprodiicer adapted to be used in the output of conventional receiverswhose armature or moving element is not limited in action by the polepieces or other obstruction when strong currents are applied to thewindings. I

Another object is to provide a method by means of which, if so; desired,all signals, speech, music, etc. are limited in volume to apredetermined maximum amount, regardless of strength in order thatlisteners will not be annoyed when tuning in, by extremely loudstations, accidently or otherwise before the volume control is properlyadjusted.

Another object is to limit disturbances, noise, atmospherics, etc. tothis predctermined sound level.

Another object is to provide an efficient but inexpensive loud speakerdriving motor which may be easily duplicated in quantities with greatuniformity of electrical. and acoustical characteristics.

A further object isto provide avdriving unit for incorporating into acomplete loud speaker and which maybe built intoradio broadcastreceivers or readily attached to standard broadcast receivers. Otherobjects and advantages of our invention will become apparent later inthe specification. 7

As is well known in theart, standard electromagnetic telephonereceivers, While very sensitive, cannot be supplied with more than acertain amount of signal enery without the diaphragm hitting the polepieces of the magnets, making the'music or speech practi callyunintelligible and distorted, causing what is often called blasting inthe case of the reproduction of music. Many loud speakers of the pasthave used merely enlarged magnetic telephone receiver elements as themotivating unit to drivethe sound reproducing diaphragm. Probably themost Widely used driver for loud speakers in the 4, 1928. Serial No.303,8'3'8.

radio art, at present is the so-called balanced armature type'of unitwhich is subject to the same objection. Comparatively narrow energylevel is required to be furnished to the unit, above which. satisfactoryreception may not be attained, even though undulatory currents ofpractically undistorted characteristics be furnished the driving'unit.

Broadly speaking our invention conte1nplates the use of a forkedarmature so an ranged that thevmovabletips can not strike any abutmentWithin its operating range of movement.

Referring to the drawings, it will readily be appreciated that in thevarious forms our unit may be built, the vibrating armature is spacedapart from and cannot come in contact With pole pieces or other parts,regardless of the signal energy-suppliedthe system, a

and the only limiting factors are those such as affecting the burningout 'otthe magnet windingsor saturation of the vibrating armature,design features which may be predetermined and set to suit the servicefor which the unit is intended.

At the same time the units shown may be designed to be sufficientlysensitive to re spoud to very weak impulses. Thus our invention providesaloud speaker driving unit for the usual type of output circuit by meansof which satisfactory reproductionof sound may be obtained eventhoughjsupplied with widely varying energy levels, as compared to unitsnow in common use.

Fig. 1 is a side View of'one form of our invention in which theenergizing coils are mountedon the pole pieces of a permanent magnetcore and the armature has two off set arms centrally pivoted between thecoils.

Fig. 2 is an endview of the same.

Fig. 3 is a side view of another form similar to Fig. 1 but with thecoils on'or around I the armature. 1

Fig. 4 is an endview of the same.

Fig. 5 is a side View of a form inwhich the forked armature is pivotedto one pole piece of the magnet and the coils are supported in place sothatthe armature tips can vibrate Within'them. p r

Fig. 6 is an end View of the same.

similar to the ones above described.

branches or arms I iorksg, 35 are preferably connected together crosspiece 36 7 wire 37 is secured. The coils 31 and 32 are 7 Fig. 7 is aside viewof another form with a forked armature having its shank securedto one magnet pole and. two coils on the.

' differentially wound coils.

Fig.9 is a sectional view of another form hav ng magnetizing coils 1nplace oithe permanent magnet and. With. 11 Yos il i llg' forked armatureand a single energizing cqil. 10 1s a diagrammatlc vlew showing one formofoutput circuit with a reproducer according to our invention. 7

In the form shown in Figs. 1 and 2 the magnet 12 is provided with twopole pieces 13 each of which is preferably laminated to reduced ed dycurrent losses and each of which has two tips 14, 14. The armature has apivot shaft 15 with two arms 16,16 set crosswiseso that their tips arerespectively'ab'ove and below the adjacent tips of the pole pieces. Thearmature is connected in any suitable manner for instance by means of adrive, rod or wire 17 to any suitable form of diaphragm or air vibrator18. The coils 1.9 which are connected in the audio output circuit of thereceiver (not shown) may be suitably mount ed upon or around either thepolepieces of the magnet orthe armature. 'In Figs. 1 and 2 these coilsare mounted on the tips 14 of the magnet polelpieces.

The construction shown in Figs. ..3 and 1 is similar to that of FigsRland 2'except that the. coils 2O are mounted "so to surround thearmature, members, nstead ofthe pole pieces of the stationary magnet. VIn both forms of construction, however, it will be noted-that thearmature when it vibrates can not come in contact with the pole piecesof the magnet and, thereiore, there can be no blasting nor crashingsound 'even when an excessive current is applied to the circuit.

in the form shown in' Figs. Sand 6 the stationary magnet-audits polepieces are The armature shaft 21 howeverin this case mounted close tothe pole pieces 22 and the armature is provided with twoarms the tips ofwhich are located above and below respectively the tips of the polepiece 24, The pole pieces are shaped to most eil ectively coa ct withthearmature. The coils 25 are supported at 26 and the armature tipsextend through these coils. 7 in the form shown in Figs. 7 and 8 thepole pieces 30 support the coils 31, 32 and the armature 33 is supportedon the'other pole of the magnet and provided with U two Two branches orto which the drive rod or differentially wound so as toproperl'y coactwith the armature members. I 1

In the construction shown in Fig. 9 the magnet 40 may beofthenon-permanent type and provided with windings 11 for providlng thenecessary field strength. In this case the pole pieces'lQ are suitablysecured to the main part of the magnet. The magnetic armature has twotips 43. supported by-abar 4A1 also. of magnetic material which passesthrough the energizing coil 15 and the tips of th arma ur -,fo ks re arnged Close to the tips of the pole pieces 12 but in position so thatthey can not touch no matter what the vibration of the armature may be.The upper endoi the armature may be adjusted by set screws'ifi which aresupported in a strap 47. viln'ating member. g I

Fig. 10 shows a typical circuit arrangement for use with our invention.In this case the primary of the transformer fiO is' connected in theplate circuit of the output tube 51 of the receiver and the secondary is'con-.

nected by leads 52 to supply energy to actuate the armature of the motor53 to drive the diaphragm 54.

1V hile we have shown the loud speaker con- 48 is the drive rodconnected to the air.

ill;

nected with the output tube through an out- It is expected, of course,that the physical laws obtaining for loud speaker motors, known to thoseskilled in developing these units, be applied in the design of our unittogether with the output circuit for which it is intended.lit-transformer coupling is used from the output or power tube, itshould have aprnnary unpedance at very low audio frequencies,approximately equal tothe as ternal impedance of the tube. Thesecondaryof the transformer should" be equal to or match? the impedance of theactuating coil system, and should'be coupled to the primary in such a,manner that practically equal e'fiic ency of transfer obta ns over theaudio frequency spectrum. Likewise the mechanical dynamic impedance ofthe driving-system should equal that for the driven "diaphragm or othersound producing arrangement. v

' The volume obtainable before the'limiting action begins is determinedby'the' distance the armature travels towardthe field'pole until furthertravel does not reducethe air gap. hen the nearest edge'of an armaturetip is opposite an. edge of a field pole further armature "travel doesnot materially reduce the air gap which is the principal part of thereluctance of the magnetic circuit. Consequently a veryjstrong'signal'will give but little increase in volume over a Weakersignal that is strong enough to place the armature at instant-s of fullcurrent amplitude, in the position of least reluctance. The slightdifference in volume between two such signals would be due to theinertia of the stronger carrying the armature slightly past thisposition; In no case can the armature come in contact with thefieldpoles, and i if the strong signal as delivered to the loudspeakeris free from distortion, and the loud speaker is correctly designed, aspleasing reproduction will result from very strong music or speech asfrom that of moderate intensity;

, To obtain this reuslt, the air gap should be such that the maximumworking range of the armature is suitable for the services intended, i.e., home broadcast receiving as compared to a public address. service;the armature must not saturate with the strongest signal the output tubeis capable-0f delivering and the diaphragm mustnot rattle with themaximum volume that the air gap is set for. V r

WVith such a reproducer, interfering disturbances, atmospherics, etc.,are limited in Y amplitude to that of the accompanying music or speech,though initially many times stronger. Likewise the annoying effects of 1fading are partly done away with inasmuch as the amplifier may beadjusted for great sensitivity and the signal will be of practicallyconstant volume as long as it does not fall below the level necessaryfor this volume requirement.

lVe claim: 7 a

l. A loud, speaker motor comprising a magnetic core having pole piecesand coil windings and an armature supported at one end and having theother end forked and with tips disposed adjacent the pole pieces of themagnet.

2. A loud speaker motor comprising a magnetic core having polepieces-and coil Windings and an armature supported at one end and havingthe other end forked and with 3 tips disposed adjacent the pole piecesof the magnet and means for limiting the vibration of the armature.

3. A loud speaker unit having two armatures, a field magnet coactingtherewith and means comprising differential windings for simultaneouslyincreaslng the flux denslty of one armature while decreasing the fluxdensity in the other armature.

WVIL SON AULL, JR. HARRY W. HOUCK. I

